Battery voltage monitoring apparatus

ABSTRACT

A battery voltage monitoring apparatus for monitoring an assembled battery voltage, the assembled battery including a plurality of battery cells, the battery voltage monitoring apparatus including a plurality of input terminals, the plurality of input terminals being respectively coupled to the plurality of battery cells through a potential measurement line, a comparator having a hysteresis characteristic and including a first terminal and a second terminal, the second terminal receiving a reference voltage, and a current source, one end of the current source being coupled between one of the plurality of the input terminals and the first terminal.

INCORPORATION BY REFERENCE

This present application is a Continuation Application of U.S. patentapplication Ser. No. 12/007,028, filed on Jan. 4, 2008, based upon andclaims the benefit of priority from Japanese patent application No.2007-000411, filed on Jan. 5, 2007, the disclosure of which isincorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a battery voltage monitoring apparatus fordetecting battery voltage of a power supply apparatus. The batteryvoltage monitoring apparatus includes a plurality of secondary batteriesconnected in series. Particularly, this invention relates to a batteryvoltage monitoring apparatus for detecting disconnection of a singleline which is used for potential measurement.

2. Description of Related Art

An electric vehicle and hybrid vehicle are known as an eco-friendly one.In the electric vehicle and hybrid vehicle, a motor is used as drivingforce. Rechargeable secondary batteries are connected to the motor aselectric power source. A direct current supplied from the secondarybattery is converted into an alternating current, and the motor isdriven by the alternating current. High voltage is required to drive themotor. Generally, the secondary battery is formed as an assembledbattery including a plurality of battery cells connected in series.

A plurality of voltage sensors are used for detecting each battery cellvoltage in the assembled battery. A moderate number of voltage sensorsare assembled and modularized. When a large number of battery cells areconnected in series such as the electric vehicle or the like, a largenumber of voltage sensors are also provided and connected in series. Anapparatus monitoring assembled battery voltage like this is shown inJapanese Unexamined Patent Application Publication Nos. 2003-208927,2003-111284, and 2005-117780.

An apparatus for monitoring potentials of the assembled batteries isdescribed hereinafter in detail. In the apparatus, a module including aplurality of voltage sensors is configured as one semiconductor device(IC). A plurality of semiconductor devices are connected in series. Eachsemiconductor device (IC) has the plurality of battery sensors.

FIG. 11 shows a schematic view of the conventional voltage monitoringapparatus. As shown in FIG. 11, one IC is able to detect voltages offour battery cells. Each input terminal of IC is connected to a batterycell C101-C108 through lines for voltage measurement L101-L109. The IC101 in FIG. 11 operates with a positive terminal (a node N101) of thebattery cell C101 as a power supply potential and a negative terminal ofthe battery cell C104 (a positive terminal of battery cell C105, a nodeN102) as ground potential. An IC 102 is connected to the IC 101 inseries. Hence, the IC 102 operates with a positive terminal (a nodeN102) of battery cell C105 as power supply potential, and a negativeterminal (a node N103) of battery cell C108 as ground potential. Wheneach IC detects that the monitored battery cell becomes excess voltageor low voltage, the IC outputs an excess voltage detect signal or lowvoltage detect signal.

Taking IC 102 of FIG. 11 for instance, the operation of a voltage sensormodule outputting the excess voltage detect signal or low voltage detectsignal is explained. FIG. 12 shows a configuration of conventional IC102 in FIG. 11. As shown in FIG. 12, the voltage sensor module comprisesa plurality of voltage sensors SEN101-SEN104 and output logic circuitsLOG101 and LOG102. When each voltage sensor SEN101-SEN104 detects excessvoltage or low voltage of the battery cell to be monitored, the voltagesensor outputs high level signal as the excess voltage detect signal orlow voltage detect signal, for example. When any voltage sensor outputsthe excess voltage detect signal or low voltage detect signal, output ofOR circuit of output logical circuit LOG101 turns into high level fromlow level, for example. With this operation, the IC 102 outputs theexcess voltage detect signal or low voltage detect signal. When anyvoltage sensor detects low voltage, the output logic circuit LOG101outputs high level, for example. When any voltage sensor detects excessvoltage, the output logic circuit LOG102 outputs low level, for example.

For the apparatus monitoring the assembled battery voltage with theplurality of series-connected ICs, the apparatus monitoring theassembled battery voltage can be configured as follows. When a lineconnecting the battery cells and the voltage monitoring apparatus isdisconnected, the voltage sensor connected to the disconnected linemonitors abnormal potential to detect disconnection. For example, thisconfiguration is shown in our Japanese Unexamined Patent ApplicationPublication No. 2006-275928. However, for example, when the linecorresponding to a connect portion between ICs like L105 in FIG. 11 isdisconnected, there are problems as follows.

When disconnection happens to the line L105 in FIG. 11, voltage supplyfrom the battery cell is not supplied to a node N104 in FIGS. 11 and 12.Hence, current flowing out from VSS101 of IC101 flows into a VCC102 andV105 of IC 102. If the circuit is configured so that the uppermostvoltage sensor SEN101 detects a defect of excess voltage for detectingdisconnection, potential of the node N104 rises at disconnecting of theL105. The voltage sensor SEN101 detects excess voltage and logic outputof output logic circuit LOG102 is inverted. At this time, in logiccircuit LOG 102, leak current flows between VCC102 as voltage supply ofIC102 and VSS102. When leak current flows, power supply potential VCC102becomes fall and potential of node N104 becomes lower. When potential ofnode N104 becomes lower, the voltage sensor SEN101 does not detectexcess voltage. Hence, output potential becomes lower. When outputpotential of voltage sensor SEN101 becomes lower than threshold of logiccircuit LOG102, output logic circuit LOG102 outputs low level again.Hence, IC102 does not output excess voltage detect signal. As a result,disconnection cannot be detected. In some cases, after that, theoperation is repeated, that excess voltage is detected because leakcurrent is decrease. Then, there is the case in which output of theIC102 maybe switched between high level and low level.

As described above, because of disconnection of lines, a detect signalof voltage sensor module is output incorrectly. Hence, there is a case,for battery voltage monitoring apparatus, output becomes unstable.

SUMMARY

In one embodiment, there is provided a battery voltage monitoringapparatus monitoring an assembled battery voltage, the assembled batteryincluding a plurality of battery cells, includes; a voltage sensordetecting potential of the plurality of battery cells; an output logiccircuit outputting a potential detect signal based on an output ofvoltage sensor, the potential detect signal representing that abnormalpotential is detected; and a delay circuit adding certain delay to theoutput of the voltage sensor and outputting the delayed voltage detectsignal to the output logic circuit; in which, the voltage sensorincludes at least one comparator having hysteresis characteristic, anddetects the potential of the battery cell based on an output of thecomparator.

In another embodiment, there is provided a battery voltage monitoringapparatus monitoring an assembled battery voltage, the assembled batteryincluding a plurality of battery cells, includes; a voltage sensordetecting potential of the plurality of battery cells; an output logiccircuit outputting a potential detect signal based on an output ofvoltage sensor, the potential detect signal representing that abnormalpotential is detected; and a delay circuit adding certain delay to theoutput of the voltage sensor and outputting the delayed voltage detectsignal to the output logic circuit; in which, the voltage sensorincludes a comparator operating with output potential of battery cell aspotential source, the battery cell being an object to be monitored, andthe comparator has hysteresis characteristic.

In still another embodiment, there is provided a battery voltagemonitoring apparatus monitoring an assembled battery voltage, theassembled battery including a plurality of battery cells, includes; acomparator detecting potential of the battery cell, and outputting apotential signal representing results of detection based on certainhysteresis characteristic; a delay circuit adding certain delay to thepotential signal; and a logic circuit outputting a potential detectsignal based on an output of the delay circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, advantages and features of the presentinvention will be more apparent from the following description ofcertain preferred embodiments taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic diagram of a voltage monitoring apparatuscomprising function of detecting disconnection;

FIG. 2 is a circuit diagram of the voltage monitoring apparatuscomprising function of detecting disconnection;

FIG. 3 is a circuit diagram of the voltage monitoring apparatusaccording to a first embodiment in this invention;

FIG. 4A is a drawing of operation waveform of the voltage monitoringapparatus according to the first embodiment in this invention;

FIG. 4B is a drawing of operation waveform of the voltage monitoringapparatus for reference;

FIG. 5 is a drawing of a voltage monitoring apparatus according to asecond embodiment in this invention;

FIG. 6 is a drawing of the voltage monitoring apparatus according to thesecond embodiment in this invention;

FIG. 7 is an operation waveform of the voltage monitoring apparatusaccording to the second embodiment in this invention;

FIG. 8 is a diagram of a variant embodiment of the voltage monitoringapparatus in this invention;

FIG. 9 is a diagram of a voltage monitoring apparatus according to athird embodiment in this invention;

FIG. 10 is a diagram of a level shift circuit according to the thirdembodiment;

FIG. 11 is a drawing of a conventional voltage monitoring apparatus; and

FIG. 12 is a drawing of a conventional voltage monitoring apparatus.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will now be described herein with reference toillustrative embodiments. Those skilled in the art will recognize thatmany alternative embodiments can be accomplished using the teachings ofthe present invention and that the invention is not limited to theembodiments illustrated for explanatory purposes.

First Embodiment

Hereinafter, embodiments of this invention are described with drawings.FIG. 1 shows a schematic diagram for explaining a voltage monitoringapparatus 10 according to the first embodiment of the invention. Thevoltage monitoring apparatus 10 of this embodiment includes a pluralityof voltage sensor modules. Here, the voltage sensor module is defined asan electrical element including one or more voltage sensors. In thisembodiment, one module is configured as one semiconductor device (IC).FIG. 1 shows an instance of the voltage monitoring apparatus 10including two voltage sensor modules IC1 and IC2. Hereinafter, thevoltage sensor module is also called IC. Hereinafter, with taking a casein which one IC detects four battery cell voltages as an example, afirst embodiment will be described.

As FIG. 1 shows, in this embodiment, eight battery cells C1-C8, whichare objects to be monitored by the voltage monitoring apparatus, areconnected in series. The IC1 operates on the condition that a positiveterminal potential of battery cell C1 (see a node N1 in FIG. 1) is afirst source potential (a higher source potential) and a positiveterminal potential of battery cell C5 (see a node N2 in FIG. 1) is asecond source potential (a lower source potential). Because the IC2 isconnected to the IC1 in series, the IC2 operates on the condition that apositive terminal potential of battery cell C5 (see a node N2 in FIG. 1)is a first source potential and a negative terminal potential of batterycell C8 (see a node N3 in FIG. 1) is a second source potential (a groundpotential).

Each positive terminal of battery cells is connected to input terminalsV1-V8 of IC through each line L1-L8. As shown in FIG. 1, the inputterminals V1-V4 are input terminals of IC1, and the input terminalsV5-V8 are input terminals of IC2. As described above, the IC1 operateson the condition that the positive terminal potential of battery cell C1is the first source potential. Hence, the positive terminal of batterycell C1 is also connected to a first source terminal VCC1 of batterycell IC1 through line L1. In other words, the line L1 also functions asa source line for the voltage sensor module IC1. As the positiveterminal potential of battery cell C5 is the second source potential forIC1 and the first source potential for IC2, the positive terminal ofbattery cell C5 is connected to a second source terminal VSS1 of IC1,the first source terminal VCC2 of IC2, and the input terminal V5 of IC2through line L5. That is, the line L5 functions as a source line for IC1and IC2. A negative terminal of battery cell C8 is connected to a secondsource terminal VSS2 of IC2 through a source line L9.

FIG. 1 shows the voltage monitoring apparatus comprising a function fordetecting disconnection for example. The voltage monitoring apparatus inFIG. 1 is based on our earlier Patent Application Publication No.2006-275928. Firstly, with reference to FIG. 1 and FIG. 2, the ICcomprising the function of detecting disconnection in the earlierpublication will be described briefly. FIG. 2 shows an IC1 based on theearlier publication.

As shown in FIG. 2, the IC of the first embodiment comprises constantcurrent sources Iref1-Iref4 corresponding to the number of the monitoredbattery cells. The IC also comprises voltage sensors SEN1-SEN4corresponding to the number of battery cells. Each voltage sensorcomprises a voltage divider resistor for excess voltage detection, avoltage divider resistor for low voltage detection, a referencepotential circuit, a comparator for excess voltage detection, and acomparator for low voltage detection. An explanation about detailedoperation of the voltage sensor is omitted. In the voltage sensors usedin this embodiment, there is no or little current change like leakcurrent caused by potential detection.

In the IC1 as shown in FIG. 2, the constant current source Iref1supplies a constant current Iref from the source terminal VCC1 of IC1 tothe input terminal V2 connected to the negative terminal of battery cellC1. The constant current source Iref2 supplies a constant current Ireffrom the source terminal VCC1 of IC1 to the potential input terminal V3connected to the negative terminal of battery cell C2. The otherconstant current sources are sequentially connected in the same way. Theconstant current source Iref4 supplies a constant current from the firstsource terminal VCC1 to the second source terminal VSS1. The IC2comprises constant current sources Iref5-Iref8 as the IC1. But, theconstant current sources of IC2 are connected so that current flows frominput terminals V6-V8 to the second source terminal VSS2 (see FIG. 1). Aswitch SW1 (a switch SW2) is provided to a current path between thefirst source terminal VCC1 of IC1 (the first source terminal VCC2 ofIC2) and the second source terminal VSS1 (VSS2). The switch SW1 (theswitch SW2) makes current of constant current source Iref4 (Iref8) toselectively flow. As shown in FIG. 1, in this embodiment, the switch SW1of IC1 is set to be conduction state, and the switch SW2 of IC2 is setto be non-conduction state.

Hereinafter, the IC1 in FIG. 2 is described as an example. During normaloperation, current Iref generated by the constant current source flowsthrough the input terminals V2-V4, VSS1, and lines L2-L5 to the negativeterminal of battery cell (see an arrow in FIG. 2). That is, in thisembodiment, when there is no disconnection in lines L1-L8, current Irefgenerated by constant current source constantly flows into each inputterminal.

When disconnection is caused in the line L3, current, which has flowedfrom VCC1 to V3, does not flow into the input terminal V3, but it flowsinto voltage sensor side (see a dashed arrow in FIG. 2). As a result,node potential (see M in FIG. 2) between the voltage sensors rises andthe voltage sensor outputs a value which is not detected during normaloperation. With this operation, disconnection of lines connected betweenthe battery cells and the voltage monitoring apparatus can be detected.

Hereinafter, the description will be made on the case in which the lineL5 is disconnected in the voltage sensor module. As described above, theconstant current source Iref4 is provided between the VCC1 and VSS1 ofIC1, and the switch SW1 is set to be conduction state. Hence, if theline L5 does not come down, the current Iref generated by Iref4 flows toa negative terminal side of the battery cell C4 through the sourceterminal VSS1 and L5. On the other hand, when disconnection is caused inthe line L5, current which is generated by Iref4 flows toward the inputterminal V5 (node N4) and VCC2 of IC2. Therefore, potential of the inputterminal V5 rises, and potential between the input terminals V5 and V6rises. That is, in the voltage monitoring apparatus 10 configured asFIG. 1, when disconnection is caused in the line L5 connected to sourcepotential of voltage sensor module, potential of input terminal V5becomes increase.

In the voltage monitoring apparatus configured as described above, thevoltage sensor module in this embodiment is configured as follows. FIG.3 shows the voltage sensor module IC2 of the first embodiment of thisinvention. Hereinafter, in drawings used for explaining the embodiments,if not otherwise specified, the current source for detectingdisconnection as described above is omitted. However, the current sourcefor detecting disconnection is actually connected. FIG. 3 shows the casein witch disconnection is caused in the line L5.

As shown in FIG. 3, the voltage sensor module IC2 comprises a pluralityof voltage sensors SEN1-SEN4, and output logic circuits LOG1 and LOG2.Each voltage sensor detects excess voltage and low voltage of batterycell, so as to output the excess voltage signal and the low voltagesignal. When the lines L5-L9 to connect the battery cells and thevoltage sensor modules come down, each voltage sensor also detectsabnormal potential and outputs the excess voltage signal and the lowvoltage signal. Hereinafter, in order to distinguish the excess voltagedetect signal from low voltage detect signal output from IC1 and IC2,detect signals output from comparators are simply called as excessvoltage signal and a low voltage signal or potential signal. When anyvoltage sensor outputs the excess voltage signal or the low voltagesignal, the output logic circuit LOG1 or LOG2 outputs the excess voltagedetect signal or the low voltage detect signal as IC2 based on thevoltage signal of the voltage sensor. In this embodiment, the outputlogic circuit comprises an OR circuit and a plurality of invertors whichoperate between VCC2 and VSS2.

Each voltage sensor SEN1-SEN4 comprises a voltage divider resistor forlow voltage detection R1, a voltage divider resistor for excess voltagedetection R2, a reference potential circuit VREF, a comparator for lowvoltage detection CMP1, and a comparator for excess voltage detectionCMP2. The comparator for excess voltage detection CMP2 compares adivided point potential (described as A in FIG. 3) of the voltagedivider resistor for excess voltage detection R2 and an output potentialVref of reference potential circuit VREF. When the divided pointpotential is higher than the output potential Vref, the comparator forexcess voltage detection CMP2 outputs the excess voltage signal. In thesame way, the comparator for low voltage detection CMP1 compares apotential of the divided point voltage of the voltage divider resistorfor low voltage detection R1 and the output potential Vref of thereference potential circuit. When the divided point potential is lowerthan the output potential Vref, the comparator for low voltage detectionCMP1 outputs the low voltage signal. The comparators CMP1 and CMP2 aredriven with operation potential between VCC2 and VSS2.

In this embodiment, the voltage sensor SEN1 which is the uppermostvoltage sensor of IC2 further comprises a switch for hysteresis HSW1.This switch HSW1 operates based on the output of the comparator forexcess voltage detection CMP2. In this embodiment, the switch forhysteresis HSW1 is connected so that a part of resistors between adivided point A and the node N4 is shorted. For example, when thecomparator for excess voltage detection outputs high level signal, theswitch for hysteresis HSW1 is set to be conduction state. Hence, outputof comparator for excess voltage detection CMP2 has hysteresischaracteristic. That is, a comparator having hysteresis characteristicis configured with the switch HSW1, the uppermost resistor of resistorR2 and the comparator for excess voltage detection CMP2. A delay circuitD1 is provided between the comparator for excess voltage detection CMP2of uppermost voltage sensor SEN1 and the output logic circuit LOG2.

Hereinafter, operations of voltage monitoring apparatus 10 configureddescribed above will be explained. FIG. 4A shows a node N4 potential(terminal V5), a divided point A potential, output of comparator forexcess voltage detection CMP2 in the voltage sensor SEN1, output ofoutput logic circuit LOG2 and leak current flowing through the outputlogic circuit. FIG. 4A shows waveforms of these signals on the conditionin which the line L5 is disconnected in this embodiment. FIG. 4B showswaveforms when there is not switch for hysteresis HSW1 and the delaycircuit D1 in this embodiment for the sake of comparison. A voltage F inFIG. 4B corresponds to the node N4 potential in FIG. 4A, a voltage G tothe divided point A potential, a voltage H to the output of comparatorfor excess voltage detection, a voltage I to the output of output logiccircuit, and a voltage J to the leak current of output of output logiccircuit. Each voltage f-j in FIG. 4B shows enlarged portion of thevoltage F-J.

It is assumed that the line L5 comes down at the time T1 in FIG. 4A.When disconnection is caused in the line L5 at the time T1, the node N4potential becomes to increase with the current source Iref4. The dividedpoint A potential rises based on the increase of node N4 potential.Hence, when the divided point A potential is higher than the referencepotential Vref at a time T2, output of comparator for excess voltagedetection turns high level (see output of comparator for excess voltagedetection in FIG. 4A).

Because output of comparator for excess voltage detection is high level,the switch for hysteresis HSW1 becomes conduction state. As part ofresistors between the node N4 and the divided point A is shorted by theswitch HSW1, the divided point A potential rises (see divided point Apotential in FIG. 4A).

Output of comparator for excess voltage detection CMP2 is input to theOR circuit of output logic circuit LOG2 through the delay circuit D1. Asthe delay circuit D1 is provided between the comparator for excessvoltage detection CMP2 of voltage sensor SEN1 and the output logiccircuit LOG2, the OR circuit of output logic circuit LOG2 outputs highlevel at the time T3 (see output of output logic circuit). At the timeT3, a certain time is passed from when the comparator for excess voltagedetection CMP2 outputs high level.

At this time, leak current flows between VCC2-VSS2 (see leak current ofoutput logic circuit), and the VCC2 potential becomes low. Hence, thenode N4 potential connected to the VCC2 becomes low. The divided point Apotential becomes low as potential of the node N4 falls. However, inthis embodiment, when the comparator for excess voltage detection CMP2outputs high level at the time T2, the switch for hysteresis HSW1 turnsconduction state. This operation sets the divided point A potentialincrease. Hence, even if leak current flows to the output logic circuit,the divided point A potential does not become Vref or below. Further,change does not occur in the output of comparator for excess voltagedetection CMP2 (see divided point A potential and output of output logiccircuit in FIG. 4A).

On the other hand, it is assumed that there is no delay circuit D1 asFIG. 4B, the comparator for excess voltage detection CMP2 outputs highlevel, and almost at the same time, the OR circuit outputs high level.The comparator for excess voltage detection detects excess voltage, andat the same time, leak current flows. As a result, this leak currentmakes VCC2 low. In this configuration, because of lowering of VCC2caused by leak current, divided potential becomes Vref or below. Hence,output of comparator for excess voltage detection oscillates and itmakes operation unstable. The voltages f-j of FIG. 4B is waveformsaround time T2, when output of comparator for excess voltage detectionoscillates. As shown in upper portion of chart, in this case, output ofcomparator for excess voltage detection turns high level and low levelrepeatedly, because the divided point A potential increases anddecreases from reference potential Vref. As a result, operations becomeunstable.

As described above, in this embodiment, hysteresis characteristic is setfor the voltage sensor SEN1 corresponding to a connect portion betweenICs. And after the predefined time is passed from when the comparatorfor excess voltage detection detects excess voltage (after outputtingthe excess voltage signal), output of output logic circuit is set to beinverted. This operation can prevent the false operation as follows fromtaking place. The voltage monitoring apparatus can not detectdisconnection caused by leak current flowing into output logic circuitLOG2 and unstable output is caused.

Second Embodiment

FIG. 5 shows a voltage monitoring apparatus according to a secondembodiment in this invention. FIG. 5 shows the voltage monitoringapparatus of second embodiment comprising IC3, which has the sameconfiguration as IC1, connected to the IC2 of FIG. 1 and FIG. 3.Hereinafter, the case will be explained in witch disconnection is causedin a line L9 corresponding to the connect portion between IC2 and IC3 inthis voltage monitoring apparatus 20.

When the line L9 comes down, current from positive terminal of batterycell C9 does not flow into current sources Iref9-Iref12 of IC3. Whendisconnection is caused in the line L9, current from VSS2 terminal (nodeN5) flows into Iref9-Iref12. Hence, VSS2 terminal potential becomeslower and potential between V8 and VSS2 in IC2 becomes larger. As aresult, a voltage sensor connected between V8 and VSS2 of IC2 detectsexcess voltage and outputs the excess voltage detect signal. Thisembodiment prevents false operation of IC2.

FIG. 6 shows a circuit diagram of IC2 according to the secondembodiment. In this embodiment, in addition to the voltage sensor SEN1,a switch for hysteresis HSW2 is provided also in a voltage sensor SEN4.A delay circuit D2 is provided between output of comparator for excessvoltage detection CMP2 of a voltage sensor SEN4 and output logic circuitLOG2. For explaining, a part of numbers is omitted. FIG. 6 has the sameconfiguration as the circuit in FIG. 3 except the switch HSW2 and thedelay circuit D2.

In this embodiment, when the comparator for excess voltage detection ofvoltage sensor SEN4 outputs detection of excess voltage as the firstembodiment, the switch for hysteresis HSW2 turns conduction state. FIG.7 shows a node N5 potential, a divided point B potential, outputpotential Vref of reference potential circuit VREF, output of comparatorfor excess voltage detection CMP2 in the voltage sensor SEN4, output ofoutput logic circuit LOG2, and leak current flowing into output logiccircuit on the condition that disconnection happens to the line L9 inthe voltage monitoring apparatus 20 of the second embodiment.

It is assumed that disconnection is caused in the line L9 in FIG. 6 atthe time T21 of FIG. 7. When disconnection is caused in the line L9 atthe time T21, the node N5 potential becomes down based on the currentsource IC3. The reference potential Vref and the divided point Bpotential fall down according to fall of node N5 potential (terminalVSS2 potential). At this time, falling gradient of node N5 potential hasslower pace than the reference potential Vref because of the potentialdivide resistor R2 (see divided point B potential in FIG. 7). When thedivided point B potential becomes higher than Vref at the time T22,output of comparator for excess voltage detection CMP2 becomes highlevel (see output of comparator for excess voltage detection in FIG. 7).

Because output of comparator for excess voltage detection becomes highlevel, the switch for hysteresis HSW2 turns conduction state. With theswitch for hysteresis HSW2, a part of resistors between the terminal V8and the divided point B potential is set to be shorted. Hence, thedivided point B potential increases at the time T22 (see divided point Bpotential in FIG. 7).

Output of comparator for excess voltage detection CMP2 is input to theOR circuit of output logic circuit LOG2 through the delay circuit D2.The delay circuit D1 is provided between the comparator for excessvoltage detection CMP2 of voltage sensor SEN4 and the output logiccircuit LOG2. Hence, the OR circuit of output logic circuit LOG2 outputshigh level at the time T23. At the time T23, a certain time is passedfrom when the comparator for excess voltage detection 24 outputs highlevel (see output of output logic circuit).

At this time, leak current flows between VCC2 and VSS2 (see leak currentof output logic circuit in FIG. 7) and VSS2 and Vref rise. However, inthis embodiment, when the comparator for excess voltage detection CMP2outputs high level at the time T2, the switch for hysterisis HSW2becomes conduction state. This operation sets the divided point Bpotential increase. Hence, even if leak current flows into the outputlogic circuit LOG2, the divided point B potential does not become Vrefor below, and output of comparator for excess voltage detection CMP2does not change (see divided point B potential and output of outputlogic circuit in FIG. 7).

As described above, this invention can be applied to the voltage sensorSEN4 connected to the line, which is the connect portion between IC2 andlower voltage sensor module (IC3). It can prevent false operation ofvoltage sensor module.

Variant Embodiment 1

FIG. 8 shows a variant embodiment of voltage monitoring apparatusaccording to embodiments of this invention. The variant also hasfunction of detecting disconnection. This embodiment differs from thefirst and the second embodiments in the way of detecting disconnection.In the voltage monitoring apparatus shown in FIG. 8, a resistor isconnected between input terminals of voltage sensor. The value ofresistor R3 connected between input terminals of voltage sensor SEN1 isdifferent from the value of resistor R4 connected between inputterminals of voltage sensor SEN2. The resistors R3 and R4 are connectedalternately between input terminals of the other voltage sensors below.

Hereinafter, operation of detecting disconnection in the voltagemonitoring apparatus configured as described above is explained. Theresistor R4 having low resistance value is connected to a forth voltagesensor which is not shown of IC1. The resistor R3 having high resistancevalue is connected to the voltage sensor SEN1 in FIG. 8. For example, ifdisconnection is caused in the line L5, on the condition that resistancevalue connected to resistors R3 and R4 in parallel is sufficientlylarge, the node N4 potential becomes the divided potential, divided byresistance ratio of resistors R3 and R4 between potential difference oftwo battery cells C4 and C5. Therefore, when the resistor value ofresistor R3 is larger, the node N4 potential rises and excess voltage isdetected.

When excess voltage is detected based on disconnection as describedabove, setting hysteresis, operation of delay circuit and else forstabilizing output of IC2 is the same as the circuit shown in FIG. 3.Hence, explanation of setting hysteresis, operation of delay circuit andelse is omitted.

The case in which potential is detected based on potential change causedby current source is described as above. However, this invention can bealso applied to the other case.

Third Embodiment

FIG. 9 shows a voltage monitoring apparatus according to a thirdembodiment. In the first and second embodiments as described above, thecase is explained in which the comparator for excess voltage detectionCMP2 operates between the potential source VCC2 and VSS2 of voltagesensor module (IC2). On the other hand, in this embodiment, thecomparator for excess voltage detection CMP2 and the comparator for lowvoltage detection CMP1 operate with potential source of one batterycell. FIG. 9 shows the case in which disconnection is caused in the lineL2 of voltage monitoring apparatus connected as shown in FIG. 1, forexample. In this case, the terminal V2 potential rises with the currentsource Iref1 and excess voltage is detected.

When the comparators for low voltage detection CMP1 and excess voltagedetection CMP2 operate with potential source of one battery cell,outputs of those become the terminal V2 potential at high level, and theterminal V3 potential at low level. However, the output logic circuitsLOG1, LOG2, which are connected to output side, operate between VCC1 andVSS1. Output of comparator, operating with potential difference of onebattery cell, can not drive the output logic circuit. Hence, in thisembodiment, the level shift circuits LS1, LS2, which change potentiallevel for outputs of comparators for low voltage detection CMP1 andexcess voltage detection CMP2, are provided in the both comparators.

Hereinafter, leak current of level shift circuit will be described.False operation may be caused by leak current of level shift circuit.

FIG. 10 shows a general level shift circuit. The level shift circuitcomprises an inverter INV1, a first level shift circuit LS2 ₁, and asecond level shift circuit LS2 ₂. Taking the case in which the levelshift circuit is connected between V2 and V3 in FIG. 9 for instance.Leak current flows through the level shift circuit. The comparatoroutputs a signal of terminal V2 level as high level or a signal ofterminal V3 level as low level. Using the inverter INV1 in the levelshift circuit LS2, the signal output from the comparator is converted toa pair of complementary signals. The pair of complementary signals isinput to the first level shift circuit LS2 ₁. As the inverter INV1 isprovided between terminals V2 and V3, output level of inverter INV1 isalso terminal V2 level or terminal V3 level. The first level shiftcircuit LS2 ₁ converts terminal V2 level representing high level intoVCC1 level and outputs VCC1 level. At this time, terminal V3 levelrepresenting low level is output without being converted. When low levelis input to the second level shift circuit LS2 ₂, the second level shiftcircuit LS2 ₂ converts terminal V3 level representing low level intoVSS1 level. In this way, the level shift circuit LS2 converts the signalof terminal V2 level representing high level and the signal of terminalV3 level representing low level into the signal of VCC1 levelrepresenting high level and the signal of VSS1 level representing lowlevel and outputs them.

In the level shift circuit as described above, an inversion signal ofinput signal is generated in the first inverter. Hence, when theinverter inverts the input signal, leak current flows between V2 and V3.This leak current changes terminal V2 potential and terminal V3potential as leak current does in the other embodiments. As a result,false operation of the comparator for excess voltage detection or elsemay be caused.

In this embodiment, a switch for hysteresis HSW3 is provided so that apart of voltage divider resistor for excess voltage detection is shortedto terminal V2 side. A delay circuit is provided between the comparatorfor excess voltage detection CMP2 and the level shift circuit LS2. Whenthe comparator for excess voltage detection CMP2 outputs high level,hysteresis characteristic is given to output signal of the comparatorCMP2 with this configuration. After this operation, with outputting highlevel to the level shift circuit LS2, it can prevent false operation ofthe voltage monitoring apparatus.

In this embodiment, hysteresis is set for the comparator for excessvoltage detection in addition to the situation in which linecorresponding to connect portion between ICs is disconnected. Andcertain delay time is set before the comparator for excess voltagedetection outputs signal. Hence, it can prevent false operation of thevoltage monitoring apparatus.

In these embodiments described above, configuration of delay circuit isnot explained. However, a delay circuit configured with a plurality ofseries-connected inverters or else is not preferable because leakcurrent flows into these inverters. Hence, it is preferable that thedelay circuit using resistance component and capacitor component isapplied to these embodiments. However, if the line between output ofcomparator and input of logic circuit has predefined delay property,this portion can be used as the delay circuit.

In this embodiment, with using the switch for hysteresis, hysteresis isset for the comparator. However, if the comparator itself hashysteresis, advantages of this invention can also be obtained withoutusing the switch for hysteresis. As described above, embodiments of thisinvention are described in detail, but the configuration can be changedin many ways in this invention. For example, the case is described abovein which false operation is caused in at detecting excess voltage, butthis invention can also be applied to the operation in detecting lowvoltage.

It is apparent that the present invention is not limited to the aboveembodiment, but may be modified and changed without departing from thescope and spirit of the invention.

What is claimed is:
 1. A battery voltage monitoring apparatus monitoringan assembled battery voltage, the assembled battery including aplurality of battery cells, the battery voltage monitoring apparatuscomprising: a plurality of input terminals, the plurality of inputterminals being respectively coupled to the plurality of battery cellsthrough a potential measurement line; a comparator having a hysteresischaracteristic and comprising a first terminal and a second terminal,the second terminal receiving a reference voltage; and a current source,one end of the current source being coupled between one of the pluralityof the input terminals and the first terminal.
 2. The battery voltagemonitoring apparatus according to claim 1, further comprising: aresistor coupled between one of the plurality of the input terminals andthe first terminal; and a switch coupled between one of the plurality ofthe input terminals and the first terminal, the switch being parallel tothe resistor, wherein a control terminal of the switch is coupled to anoutput of the comparator.
 3. The battery voltage monitoring apparatusaccording to claim 1, further comprising a plurality of a currentsources that include the current source, wherein the plurality of thecurrent sources are respectively coupled to the plurality of the inputterminals.
 4. The battery voltage monitoring apparatus according toclaim 1, wherein the assembled battery include a first battery cell, asecond battery cell, and a third battery cell, wherein the plurality ofinput terminals includes a first input terminal, a second inputterminal, a third input terminal, and a fourth input terminal, whereinthe first and second input terminals receive a voltage applied betweenboth ends of the first battery cell, wherein the second and third inputterminals receive a voltage applied between both ends of the secondbattery cell, and wherein the third and fourth input terminals receive avoltage applied between both ends of the third battery cell.
 5. Thebattery voltage monitoring apparatus according to claim 4, wherein thefirst terminal of the comparator is coupled between the first inputterminal and the second input terminal.
 6. The battery voltagemonitoring apparatus according to claim 5, wherein the comparatorcomprises a first comparator, wherein the battery voltage monitoringapparatus further comprises a second comparator having a hysteresischaracteristic and comprising a third terminal and a fourth terminal,wherein the third terminal is coupled between the third input terminaland the fourth input terminal, and wherein the fourth terminal receivesa reference voltage.
 7. The battery voltage monitoring apparatusaccording to claim 4, wherein the comparator comprises: a first powersupply terminal coupled to the first input terminal; and a second powersupply terminal coupled to the fourth input terminal.
 8. The batteryvoltage monitoring apparatus according to claim 4, wherein thecomparator comprises: a first power supply terminal coupled to the firstinput terminal; and a second power supply terminal coupled to the secondinput terminal.
 9. The battery voltage monitoring apparatus according toclaim 8, further comprising a level shifter circuit coupled to an outputof the comparator.
 10. The battery voltage monitoring apparatusaccording to claim 9, further comprising an output circuit thatcomprises a third power supply terminal coupled to the first terminaland a fourth power supply terminal coupled to the fourth terminal, theoutput circuit being connected to an output of the level shiftercircuit.
 11. The battery voltage monitoring apparatus according to claim10, further comprising a delay circuit coupled between the comparatorand the output circuit.